I was told when I did my axle swap that my rear drive shaft already had 1350 u joints. I told the guy it was off a half ton chevy and he replied that he had been doin his job for 20 yrs and he was telling me the truth. Any ways I installe the rear driveshaft to the 14ff with no changes. SHorlty after that I started getting a hellacious vibration which seemed like the tranny. I was checking u joints and found the rear u joint would move up and down between the dog ears on the yoke. I had bought a spare 3/4 u joint from Napa and put it in the yoke and it did the same thing. WTF is going on??? Please help.